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package com.sun.mail.imap.protocol;

import java.io.*;

/**
 * 
 * 
 from RFC2060
 * 
 * 5.1.3. Mailbox International Naming Convention
 * 
 * By convention, international mailbox names are specified using a
 * modified version of the UTF-7 encoding described in [UTF-7]. The
 * purpose of these modifications is to correct the following problems
 * with UTF-7:
 * 
 * 1) UTF-7 uses the "+" character for shifting; this conflicts with
 * the common use of "+" in mailbox names, in particular USENET
 * newsgroup names.
 * 
 * 2) UTF-7's encoding is BASE64 which uses the "/" character; this
 * conflicts with the use of "/" as a popular hierarchy delimiter.
 * 
 * 3) UTF-7 prohibits the unencoded usage of "\"; this conflicts with
 * the use of "\" as a popular hierarchy delimiter.
 * 
 * 4) UTF-7 prohibits the unencoded usage of "~"; this conflicts with
 * the use of "~" in some servers as a home directory indicator.
 * 
 * 5) UTF-7 permits multiple alternate forms to represent the same
 * string; in particular, printable US-ASCII chararacters can be
 * represented in encoded form.
 * 
 * In modified UTF-7, printable US-ASCII characters except for "&"
 * represent themselves; that is, characters with octet values 0x20-0x25
 * and 0x27-0x7e. The character "&" (0x26) is represented by the two-
 * octet sequence "&-".
 * 
 * All other characters (octet values 0x00-0x1f, 0x7f-0xff, and all
 * Unicode 16-bit octets) are represented in modified BASE64, with a
 * further modification from [UTF-7] that "," is used instead of "/".
 * Modified BASE64 MUST NOT be used to represent any printing US-ASCII
 * character which can represent itself.
 * 
 * "&" is used to shift to modified BASE64 and "-" to shift back to US-
 * ASCII. All names start in US-ASCII, and MUST end in US-ASCII (that
 * is, a name that ends with a Unicode 16-bit octet MUST end with a "-
 * ").
 * 
 * 
 * 
 * 
 * 
 * Crispin Standards Track [Page 15]
 * 
 * RFC 2060 IMAP4rev1 December 1996
 * 
 * 
 * For example, here is a mailbox name which mixes English, Japanese,
 * and Chinese text: ~peter/mail/&ZeVnLIqe-/&U,BTFw-
 * 
 * 
 * This class will do the correct Encoding for the IMAP mailboxes
 * 
 * @author Christopher Cotton
 */

public class BASE64MailboxEncoder {
	protected byte[] buffer = new byte[4];
	protected int bufsize = 0;
	protected boolean started = false;
	protected Writer out = null;

	public static String encode(String original) {
		BASE64MailboxEncoder base64stream = null;
		char origchars[] = original.toCharArray();
		int length = origchars.length;
		boolean changedString = false;
		CharArrayWriter writer = new CharArrayWriter(length);

		// loop over all the chars
		for (int index = 0; index < length; index++) {
			char current = origchars[index];

			// octets in the range 0x20-0x25,0x27-0x7e are themselves
			// 0x26 "&" is represented as "&-"
			if (current >= 0x20 && current <= 0x7e) {
				if (base64stream != null) {
					base64stream.flush();
				}

				if (current == '&') {
					changedString = true;
					writer.write('&');
					writer.write('-');
				} else {
					writer.write(current);
				}
			} else {

				// use a B64MailboxEncoder to write out the other bytes
				// as a modified BASE64. The stream will write out
				// the beginning '&' and the ending '-' which is part
				// of every encoding.

				if (base64stream == null) {
					base64stream = new BASE64MailboxEncoder(writer);
					changedString = true;
				}

				base64stream.write(current);
			}
		}

		if (base64stream != null) {
			base64stream.flush();
		}

		if (changedString) {
			return writer.toString();
		} else {
			return original;
		}
	}

	/**
	 * Create a BASE64 encoder
	 */
	public BASE64MailboxEncoder(Writer what) {
		out = what;
	}

	public void write(int c) {
		try {
			// write out the initial character if this is the first time
			if (!started) {
				started = true;
				out.write('&');
			}

			// we write each character as a 2 byte unicode character
			buffer[bufsize++] = (byte) (c >> 8);
			buffer[bufsize++] = (byte) (c & 0xff);

			if (bufsize >= 3) {
				encode();
				bufsize -= 3;
			}
		} catch (IOException e) {
			// e.printStackTrace();
		}
	}

	public void flush() {
		try {
			// flush any bytes we have
			if (bufsize > 0) {
				encode();
				bufsize = 0;
			}

			// write the terminating character of the encoding
			if (started) {
				out.write('-');
				started = false;
			}
		} catch (IOException e) {
			// e.printStackTrace();
		}
	}

	protected void encode() throws IOException {
		byte a, b, c;
		if (bufsize == 1) {
			a = buffer[0];
			b = 0;
			c = 0;
			out.write(pem_array[(a >>> 2) & 0x3F]);
			out.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
			// no padding characters are written
		} else if (bufsize == 2) {
			a = buffer[0];
			b = buffer[1];
			c = 0;
			out.write(pem_array[(a >>> 2) & 0x3F]);
			out.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
			out.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
			// no padding characters are written
		} else {
			a = buffer[0];
			b = buffer[1];
			c = buffer[2];
			out.write(pem_array[(a >>> 2) & 0x3F]);
			out.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
			out.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
			out.write(pem_array[c & 0x3F]);

			// copy back the extra byte
			if (bufsize == 4)
				buffer[0] = buffer[3];
		}
	}

	private final static char pem_array[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
	'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
	'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
	'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
	'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
	'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
	'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
	'4', '5', '6', '7', '8', '9', '+', ',' // 7
	};
}
